<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <button>按钮</button>
    <script>
        const btn = document.querySelector('button');
        // L0事件解绑
        // btn.onclick = function () {
        //     alert('点我呀');
        //     btn.onclick = null;
        // }
        // L2事件解绑方法
        btn.addEventListener('click', function fn() {
            alert('点我呀');
            btn.removeEventListener('click', fn)
        })
    </script>
</body>

</html>